This invention relates to a device for compressing fluids (vapor and gas), by means of compressors arranged in a parallel configuration. More specifically, the present invention is directed toward an improved device for controlling oil and pressure variants contained within the parallel compressors used, for example, in refrigeration units. The improved device of the present invention may eliminate oil separators generally found in conventional refrigeration units using parallel compressors.
Refrigeration systems with refrigerant miscible with lubricating oils, are common in the refrigeration industry. To provide proper lubrication as well as continuous circulation of spanned and compressed refrigerant, both oil and refrigerant are mixed, or are miscible, while the refrigerant is in its liquid phase. Oil and refrigerant are separated once the refrigerant is placed in its vapor or gas phase. Thus, typical refrigeration systems utilize compression and expansion means whereby refrigerant is cycled between a compressed phase and an expanded phase. Expanded refrigerant allows heat transfer such that cool air can be drawn from cooling coils through which the expanded, cooled refrigerant circulates. In contrast, compressed refrigerant circulated through heating coils provides a warm exchange surface for expelling warm air outside of the conditioned air space. It is the compressed refrigerant stage, or more particularly, the compressor which constitutes the present invention.
For a compressor to operate properly during its continuous compression of refrigerant, it is necessary to control the oil flow rate and/or deposits contained within the cycled refrigerant. Overflowing (i.e., lowering of) in the level of the compressor crankcase oil can be avoided by providing the oil return through the suction line and its transference to the crankcase chamber. The transference of oil throughout the system to prevent excess oil buildup or overflowing of one portion of the system, while starving another portion, is of critical importance in the longevity and efficiency of a parallel refrigeration compressor system. In a refrigeration system with only one compressor, it is relatively easy to maintain a tolerable rate of oil in the fluid and a relatively constant level of oil in the crankcase chamber. However, the problem is aggravated by the installation of two or more compressors in parallel, mainly when the compressors have different capacities or even when some of the compressors maintain operation while others are stopped. In a parallel compressor configuration, oil leaving the crankcases does not coincide with the route taken by the oil entering the crankcases. Thus, oil often builds in one or more compressor crankcases leaving other parallel crankcases substantially void of oil. This subjects some compressors to the risk of overflowing of "liquid hammers" while subjecting others to the risk of the lack of lubrication.
The problems concerning the return and differences in the oil level in parallel compressor crankcases is spearheaded by the recent popularity of parallel compressor systems. High efficiency air conditioning units often utilize parallel compressors. However, attempts to maintain longevity and efficiency within parallel systems are compounded by the problems recited hereinabove. The solution proposed by U.S. Pat. No. 4,822,259, of the same inventor, addresses the concept of equalizing oil level and pressure between crankcase chambers. U.S. Pat. No. 4,822,259, however, requires a conventional oil separator that controls the rate of oil dissolved in the refrigerant as well as the levelling of oil in all of the parallel compressor crankcases composing the system.